Hypocrellins are naturally occurring perylenequinones found in various parasitic fungi, including Hypocrella bambusae and Shiraia bambusicola. The photosensitizing activity and chemical structure of hypocrellin B and a related compound hypocrellin A was first described in 1992 (Nenghui et al., 1992, J. Photochem Photobiol B 14(3):207-17). These and other related hypocrellins (C, D) and perylenequinones have subsequently been identified in other species of fungi. Phleichrome, a perylenequinone, is a known natural product initially isolated from the mycelium of C. phlei. 
Hypocrellins and fungal perylenequinones have been investigated for their use as photodynamic therapy (PDT) agents, antiviral, anticancer, antimicrobial and antiparasitic activities and the like (Ma et al., 2004 Antimicrobial Agents and Chemotherapy 48:4450-4452) and derivatives exhibiting enhanced absorption at specific wavelengths (for PDT applications) have been developed (see, for example, Paul et al., 2008. J. Photochem. Photobiol B 94:38-44). The availability of hypocrellins and fungal perylenequinones for these uses however, is limited by extraction from the fungi that produce it, or complex multi-step synthetic methods from precursors (PCT Publication WO 98/33470, U.S. Pat. No. 6,936,571, Hauser et al., 1994 J. Org Chem 59:1697-1969). Diwu et al., 1992 (Tetrahedron 48:45-54) describes a one-step coupling reaction to produce perylenequinone from 1,2 naphthoquinone.
H. bambusae has not been reported as successfully grown in culture, thus its role as a source of hypocrellin is limited to its harvest in China. Other fungi that produce perylenequinones have been successfully grown in culture. For example, Seto et al (2005, Biosci. Biotechnol. Biochem 69(8):1515-1519; which is incorporated herein by reference) observed that Timothy plants infected by the fungus Epichloe typhina are resistant to disease caused by the C. phlei fungus, and identified metabolites (cyclo-(L-Pro-L-Leu) and cyclo-(L-Pro-L-Phe) that stimulate C. phlei to produce phleichrome. A publication by Lee et al., (2007, Biotechnology and Bioprocess Engineering 12:505-518; which is incorporated herein by reference) describes culture conditions and extraction of phleichrome from C. phlei. A recent publication by Kim et al. (2009, Plant Pathol J. 25:179-183; which is incorporated herein by reference) has described a transformation protocol for genetic manipulation of C. phlei, which may be useful for development of fungal strains that are enhanced for production of phleichrome or other perylenequinones.
Synthesis of hypocrellin B from precursors is complicated as illustrated by PCT publication WO 98/33470; and extraction from natural sources may not provide sufficient product for widespread use in pharmaceuticals. A more expedient method of obtaining hypocrellin B would be advantageous.